T helper type 1 (Th1) development is facilitated by interrelated changes in key intracellular factors, particularly signal transducer and activator of transcription (STAT)4, T-bet, and GATA-3. Here we show that CD4+ cells from T-bet−/− mice are skewed toward Th2 differentiation by high endogenous GATA-3 levels but exhibit virtually normal Th1 differentiation provided that GATA-3 levels are regulated at an early stage by anti–interleukin (IL)-4 blockade of IL-4 receptor (R) signaling. In addition, under these conditions, Th1 cells from T-bet−/− mice manifest IFNG promotor accessibility as detected by histone acetylation and deoxyribonuclease I hypersensitivity. In related studies, we show that the negative effect of GATA-3 on Th1 differentiation in T-bet−/− cells arises from its ability to suppress STAT4 levels, because if this is prevented by a STAT4-expressing retrovirus, normal Th1 differentiation is observed. Finally, we show that retroviral T-bet expression in developing and established Th2 cells leads to down-regulation of GATA-3 levels. These findings lead to a model of T cell differentiation that holds that naive T cells tend toward Th2 differentiation through induction of GATA-3 and subsequent down-regulation of STAT4/IL-12Rβ2 chain unless GATA-3 levels or function is regulated by T-bet. Thus, the principal function of T-bet in developing Th1 cells is to negatively regulate GATA-3 rather than to positively regulate the IFNG gene.

Infliximab is not superior to placebo in preventing clinical recurrence after CD-related resection. However, infliximab does reduce endoscopic recurrence. ClinicalTrials.gov ID NCT01190839.

Among patients who started vedolizumab for active inflammatory bowel disease, clinical remission rates are 21-25% after 54 weeks.

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The Th1 and Th2 T cell responses that underlie inflammatory bowel diseases (IBDs) are likely to depend on NF-κB transcriptional activity. We explored this possibility in studies in which we determined the capacity of NF-κB decoy oligodeoxynucleotides (decoy ODNs) to treat various murine models of IBD. In initial studies, we showed that i.r. (intrarectal) or i.p. administration of decoy ODNs encapsulated in a viral envelope prevented and treated a model of acute trinitrobenzene sulfonic acid-induced (TNBS-induced) colitis, as assessed by clinical course and effect on Th1 cytokine production. In further studies, we showed that NF-κB decoy ODNs were also an effective treatment of a model of chronic TNBS-colitis, inhibiting both the production of IL-23/IL-17 and the development of fibrosis that characterizes this model. Treatment of TNBS-induced inflammation by i.r. administration of NF-κB decoy ODNs did not inhibit NF-κB in extraintestinal organs and resulted in CD4 + T cell apoptosis, suggesting that such treatment is highly focused and durable. Finally, we showed that NF-κB decoy ODNs also prevented and treated oxazolone-colitis and thus affect a Th2-mediated inflammatory process. In each case, decoy administration led to inflammation-clearing effects, suggesting a therapeutic potency applicable to human IBD.

The actin ADP-ribosylating Clostridium botulinum C2 toxin is a binary toxin composed of the binding component C2II and the enzyme component C2I. C2I ADP-ribosylates G-actin at arginine 177, resulting in the depolymerization of the actin cytoskeleton. Here, we studied the structure-function relationship of C2I by site-directed mutagenesis. 299, which are conserved in various prokaryotic and eukaryotic argininemodifying ADP-ribosyltransferases, are essential for ADPribosyltransferase activity of the enzyme component of C. botulinum C2 toxin.Various bacterial exotoxins ADP-ribosylate eukaryotic proteins. These proteins are essential for signal transduction or cellular structure. With respect to their protein substrates, these toxins can be classified into at least four groups: (i) elongation factor 2 ADP-ribosylating toxins (e.g. diphtheria toxin) (1); (ii) heterotrimeric G-protein ADP-ribosylating toxins (e.g. cholera and pertussis toxin) (2); (iii) toxins (e.g. Clostridium botulinum C3 exoenzyme) that ADP-ribosylate small GTPases (3); and (iv) ADP-ribosyltransferases with actin as a substrate (4). The fourth group includes the clostridial ADPribosyltransferases C. botulinum C2 toxin (5), Clostrium perfringens iota toxin (6), Clostridium spiroforme toxins (7), and an ADP-ribosyltransferase from Clostridium difficile (8).The binary C. botulinum C2 1 toxin is composed of the binding component C2II (M r ϳ100,000) and the enzymatic component C2I (M r ϳ49,000). Both components are separate proteins and are neither covalently nor noncovalently linked (9). To elicit toxic effects, the trypsin-activated C2II (M r ϳ80,000) binds to the cell surface and forms a binding site for C2I (10). The toxin enters the cell via receptor-mediated endocytosis (11) followed by translocation of C2I into the cytosol. In the cell, the enzyme component ADP-ribosylates G-actin at arginine 177 (5, 12). Substrates of C2 toxin are ␤/␥-non-muscle actin and ␥-smooth muscle actin, but not ␣-actin isoforms. In contrast to C2 toxin, the related iota toxin ADP-ribosylates all actin isoforms (13). ADP-ribosylation inhibits actin polymerization and blocks the actin ATPase activity (5, 14). Moreover, ADP-ribosylation turns G-actin into a capping protein that binds to the fast-growing (barbed) ends of F-actin, which inhibits polymerization of nonmodified actin at these ends (15). Finally, ADPribosylation of actin blocks the nucleation activity of the gelsolin-actin complex (16). In intact cells, C2 toxin causes complete depolymerization of the actin cytoskeleton and eventually cell death (17).Despite a rather poor amino acid sequence homology between the various bacterial ADP-ribosyltransferases, recent crystallographic data revealed a very similar tertiary structure between Pseudomonas aeruginosa exotoxin A (18), diphtheria toxin (19), Escherichia coli heat-labile enterotoxin (20), and pertussis toxin (21). The NAD-binding and catalytic site, which is formed by two antiparallel ␤-sheets flanked by two ␣-helices, appears to be highly conserved among all ...

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